Heterogeneous catalysts have been used widely in the refining and chemical processing industries for many years to facilitate and/or speeding chemical reactions. Most catalysts used in refining industry are metal supported catalysts containing one or more noble metals like platinum, palladium, silver, rhodium, iridium etc. Among these, platinum-tin based catalysts are used for petroleum refining process. Control over morphology and composition of catalysts is of particular interest in petrochemical research as it influences their activity, selectivity and affects the economy largely. In aromatics plant, catalysts are used in continuous catalytic regeneration (CCR) type reforming processes. During its use, the coke deposition occurs on the catalytically active metal surface thereby reducing their catalytic activity. Hence, the catalysts are required to be regenerated for their reuse in plant. Presently, carbon deposition (coking-the blocking of metal surface by accumulation of carbon on metal) and sintering (the formation of large metal particles, which lower overall surface area and activity) of the active catalyst constituent have been identified as main deactivation process in high temperature reaction with the heterogeneous catalyst.
Owing to higher cost of the noble metal catalyst, and the aforementioned problem of frequent regeneration, minor improvement in the conversion yield as well as the life span of the catalyst has been targeted ever since. To address the deactivation of heterogeneous catalyst occurs through coking, the bimetallic catalyst have been produced; wherein, the cost of the active metal is reduced by replacing some of the atoms by less expensive alternative transition metals. Furthermore, the bimetallic catalysts govern the higher selectivity for the product due to synergic effect of differences in the adsorption energies over the surface of constituent elements and their electronic properties. Previously, atomic layer deposition method have been commonly used to functionalize the catalytic materials or substrates; wherein, the liquid precursors are decomposed at higher temperature and their vapours are deposited on target materials under vacuum condition. The atomic layer deposition on the materials is carried out in specially designed chemical reactor; wherein, temperature and vacuum are controlled in predicted manner. This ALD method was previously used for functionalizing the catalysts such as Pd with Al2O3, Pt—Re with Al2O3 or Pt—Ir with Al2O3. US 2008/0038463 A1 also relates to a method for depositing a material on a substrate during an atomic layer deposition (ALD) process which includes positioning the substrate on a substrate support within a process chamber, flowing a carrier gas into an expanding channel to form a circular flow of the carrier gas, exposing the substrate to the circular flow, and depositing a material onto the substrate. The method further provides that the process chamber has a chamber lid containing a centrally positioned expanding channel, a tapered bottom surface extending from the expanding channel to a peripheral portion of the chamber lid, at least two gas inlets in fluid communication with the expanding channel, and at least two conduits positioned to provide a gas flow having a circular pattern within the expanded channel. Thus, the process requires complex processing chamber and specifically designed reactor for carrying out the ALD process. U.S. Pat. No. 6,305,314 B1 also relates to a method and apparatus for avoiding contamination of films deposited in layered depositions, such as Atomic Layer Deposition (ALD) and other sequential chemical vapor deposition (CVD) processes, wherein CVD-deposited contamination of ALD films is prevented by use of a pre-reaction chamber that effectively causes otherwise contaminating gaseous constituents to deposit on wall elements of gas-delivery apparatus prior to entering the ALD chamber. Further, other prior work such as
Rev. Sci. Instrum., Vol. 73, No. 8, August 2002, 2981; and Chem. Soc. Rev., 2011, 40, 5242-5253 also provides complex procedures for coating of catalyst surface and thereby requiring sophisticated apparatus/system for workability, which are inconvenient for scaling-up. Similarly, articles in Science 335, 1205 (2012) and Catalysis Letters 141, 512 (2011) also provide specific systems and reactors for carrying out surface layering of metallic catalysts.
As can be observed, most of the processes known in the aforementioned prior arts provide processes which have specific procedural requirements and/or high energy requirements. Therefore, carrying out such processes at a commercial scale for the large quantity of catalyst spheres/extrudates is difficult and costly. Thus there is a need for an easy, economic and convenient process of layering the catalyst, which does not involve specifically designed apparatus or particularly designed reactors, and are commercially viable and scalable.